The BasicSwap docs moved to basicswapdex.com/docs. Their source now lives in the basicswapdex.com repository, under src/content/docs.
This repository serves docs.basicswapdex.com, where every old address forwards to its own page on the new site. The site/ folder is that redirect site, and .github/workflows/deploy.yml publishes it to GitHub Pages. It is generated by tools/docs-redirects.mjs in the basicswapdex.com repository, so to change a redirect, edit the map there, regenerate the site and replace site/ with the output.
The docs as they were before the move are on the legacy branch.